Materialbyelement new modifier - MCG ?

Hi,
I think this is more a MCG modifier request :
I would like to have a modifier ala Materialbyelement but where we can choose which id to change.
For example :
I have a tree, one id for trunc (1), one for branches (2) and one for leaves (3).
I would like to have a modifier where I can choose ID 3, and randomize by element to 3,4,5,6 to make random leaves.
Thanks :-)